1. Field of the Invention
The present invention relates to portable communication equipment and, more particularly to a hinge mechanism for use in a portable communication apparatus such as a portable telephone.
2. Description of the Related Art
In general, a foldable portable telephone is composed of a main body and a foldable portion which is rotatably supported on a single shaft by a hinge mechanism to rotate it between open and closed positions. A rotation of the foldable portion is preferably restricted and held at a desired angle with respect to the main body to allow stable and easy operation. There have been known a large number of single mechanisms that restrict and maintain a rotation of the foldable portion. Further preferably, a force required rotating the foldable portion between opened and closed positions is kept constant.
Such a hinge mechanism can be achieved by combining an elastic part such as a leaf spring or a coil spring and a well-known positioning and holding means using the fit between a ball and a recess. For example, Japanese Utility Model Registration No. 2525942 discloses a hinge mechanism in which a protrusion biased by a coil spring is engaged in a recess to hold the foldable part in position. Japanese Patent Unexamined Publication No. 8-218721 discloses a hinge mechanism with a fixing function in which a protrusion of a slidable cam biased by a coil spring is engaged in a recess of a fixed cam to hold the foldable part in position.
Needless to say, in the field of portable telephones, a drastic reduction in size and weight is demanded more and more. Although miniaturization of a leaf spring or a coil spring is also needed, the miniaturization makes it more difficult to provide the leaf spring or coil spring with a spring constant as large as necessary. A spring made of metal blocks weight reduction. A complicated mechanism composed of a lot of parts blocks cost reduction.